Threaded connection



y 7, 1935. m. ZELT 2,000,132

TKREADED CONNECTION Fl-led Feb. 1 1934 Inventor: I Elmer J. Zelt,

J'Z AttQbhe Patented May 7, 1935 UNITED STATES PATENT OFFICE eral Electric Company,

York

a corporation of New Application February 1, 1934, Serial No. 709,310

1 Claim.

My invention relates to insulating bushings. It is frequently desirable to secure a bushing through an opening in a thin wall of a casing such as is commonly used for a transformer. 5 A threaded connection between the bushing and easing wall is a convenient arrangement because it permits them to be quickly and easily assembled and it is simple and inexpensive. However, it is not very practicable to form a 10 helical thread on the edge of the wall around the opening if the wall is rather thin. The general object of the invention is to provide an improved form of bushing and electrical apparatus casing assembly. 15 The invention will be more fully explained in the following description taken in connection with the accompanying drawing in which Fig 1 shows a transformer in a thin sheet metal ca. ing with a small bushing secured in an open ing in the casing in accordance with the invention; Fig. 2 is an enlarged view of a small section of the casing with the opening for the bushing; Fig. 3 is an enlarged view of the bushing held in the opening; Fig. 4 is a sectional 25 view on the line 4-4 of Fig. 3; and Fig. 5 is a sectional view on the line 5-5 of Fig. 3.

Like reference characters indicate similar parts in the different figures of the drawing.

The invention will be explained in connection with a bushing I secured in an opening H in a casing I2 of a transformer I! as shown in the drawing. The bushing ID has an opening II for the transformer leads I which are peotected by the bushing from the thin edge of the opening II in the casing.

The outer end of the bushing I0 is formed with an external flange l6 and external helical threads I! are formed from this flange to the inner end of the bushing. The threaded part of the bushing I0 is turned into the opening H and held securely in place with its flange I6 against the outer surface of the casing !2. This cannot be done, however, if the opening H is round or circular because the helical threads I! 45 could not be made to enter a round opening if their diameter were at all greater than that of the opening and they would not be held in place if their diameter were at all smaller than that of the opening. The invention overcomes this difiiculty by making the opening H approximately elliptical With its minor diameter somewhat shorter than that of the threads I? and its major diameter somewhat longer than that of the threads I"! as indicated clearly in 5 Figs. 3, 4 and 5. The edge of the sheet around the opening II, at. least those portions at the ends of its minor diameter where they are engaged by the threads I1, is thinner than the pitch of the threads so as to enter the space 10 between two threads as indicated in Fig. 5. Preferably the whole sheet in which the opening H is formed is thinner than the pitch of the threads I! so that all that is necessary to form the opening is to punch it out with a simple punch of suitable cross section. As the threads I! are turned into the opening H, they engage the edge of the sheet at the opposite ends of the minor diameter of the opening as indicated in Fig. 5 but are free to pass through the opening at opposite ends of the major diameter of the opening as indicated in Fig. 4. While an approximately elliptical shaped opening II is considered preferable, other forms of opening may be used if desired so long as its minor diameter is smaller than that of the threads l1 and its major diameter is greater than that of the threads H.

The invention has been explained by describing and illustrating a particular form of bushing held in an opening in a transformer casing but it will be apparent that other forms and applications of the invention may be made without departing from the spirit of the invention and the scope of the appended claim.

What I claim as new and desire to secure by Letters Patent of the United States is:

The combination with a wall of an electrical apparatus casing, of a bushing having an externally helically threaded portion and an external flange, said wall having an opening to receive said bushing, the edge of the wall around said opening being in the plane of the wall and having a minor diameter smaller than that of the threads and a major diameter greater than that of the threads, and said wall being thinner than the pitch of the threads.

ELMER J. ZEL'I. 

